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Chewing (Less) Makes Us Human

Humans are very close, genetically, to our ape relatives. But the small differences between us are crucial. When you think about what separates humans from chimpanzees, there are probably a lot of obvious differences that spring to mind: hair, certainly, and our longer legs and bipedalism. You might think of the shape of our hands. And, of course, you might think of the differences in our head and brain shape. But you probably don’t think of the difference that makes that head and brain shape possible: we chew less than our ape relatives, which has a profound influence on essentially every aspect of our lives.

Close up of a chimpanzee

The Benefit and Cost of Chewing

Birds obviously don’t have any teeth. Have you ever wondered how they chew their food? They don’t. Some birds will swallow stones and hold them in their gullet to help grind up food. These are called gastroliths. They were also used by dinosaurs, and they’re very common finds with the remains of certain types. Lizards don’t chew their food, either. Their teeth are designed for grasping prey and maybe crunching a cricket a couple of times to make sure it’s dead before swallowing. Crocodiles will tear chunks off their prey and then down the gullet it goes.

Chewing is one of the things that distinguishes mammals from other animals. Although not all mammals chew, all the animals that chew are mammals. Chewing is great: warm-blooded creatures like us need a lot of nutrients from our food, and chewing food up allows us to extract more nutrients from it.

But this comes at a cost–it takes time to chew. A lot of time: chimpanzees spend about half their waking hours chewing, and it’s likely that our early ancestors spent about that much, too.

Breaking the Chewing Trap

But then our ancestors developed a new way of approaching our food that suddenly freed up much of our time: processing food. If you think of processed food, your mind may leap to chicken nuggets, but there are many simple processing steps that can make a big difference in how much chewing we have to do, as researchers at Harvard University discovered.

They estimated that adding meat and tubers to our diet and using simple food processing saved our ancestors an average of about 2.5 million chews per year, an 18% reduction. Using volunteers, they found that a large piece of raw goat meat was basically unchewable, but a smaller piece could be chewed just 30 times before swallowing. Suddenly, with just a few minutes of preparation, humans had gained another hour of free time that they could devote to whatever they wanted, from making or caring for babies to cave paintings to experimenting with fire.

Incidentally, cooking would be added another 1.5 million years later, about 500,000 years ago, and, it would continue to trend of less chewing.

How Less Chewing Reshaped Our Face

Remember that big snout we were talking about on chimpanzees? Our ancestors had a face like that, too, because they needed it. They needed to have room for the large muscles necessary to constantly chew roughage. But adding meat and processing food didn’t just reduce the number of chews we needed, it reduced the force needed, too.

In fact, adding meat and tubers and processing our food reduced the amount of force necessary to chew by about 25%. With about 25% less force demand on our jaw muscles, our face could shrink, creating the smaller, more controllable mouth that enables us to talk. The position of the larynx could shift, too, making speech easier.

But there are downsides to these changes in chewing. First, we no longer have room for all the teeth our ancestors needed, which is why many people need to have their wisdom teeth extracted.

And now our jaw is no longer adapted to the rigors of all-day chewing. That’s why gum chewing or clenching your jaw can damage your temporomandibular joints, which connect your jaw to your skull, resulting in temporomandibular joint disorders (TMJ).

All in all, it’s a pretty fair tradeoff, but if you find yourself suffering from these compromises, please call (619) 299-5925 for an appointment with a San Diego dentist at Strober dental who can help with TMJ or wisdom teeth problems.